Electron beam valve device



Feb. 27, 1945. NAGY ETAL 2,370,255

ELECTRON BEAM VALVE DEVICE Filed June 16, 1942 2 Sheets-Sheet 1 Feb. 27,1945. N-AGY ETAL 2,370,255

ELECTRON BEAM VALVE DEVICE Filed June 16, 1942 2 Sheets-Sheet 2 PatentedFeb. 27, 1945 ELECTRON BEAM VALVE DEVICE Paul Nagy, Richmond, and MarcusJames Goddard, Newbury, England Application June is, 1942, Serial No.447,273 In Great Britain July 7, 1941 8 Claims.

The present invention relates to electronic valve circuits employing anelectronic valve wherein an electron beam is focussed into an electronimage on an electrode and wherein output signals are developed bydeflection of the electron image across said electrode, during some partof which deflection the electron beam may partially or wholly leave theelectrode.

Various forms of electronic valve have been described in which theoutput signals are thus produced by the deflection of an electron beam,but in all these forms the essential underlying principle is that theelectron beam is deflected across a line of demarcation appertaining tothe electrode upon which the electron beam is tocussed. This electrodewill be hereinafter referred to as the output electrode. In some forms,a single homogeneous output electrode is employed. In such forms theline of demarcation is the edge of the electrode. In some forms twooutput electrodes are employed. .In such forms the line of demarcationis the line of separation of the two electrodes. In some forms oneoutput electrode is employed which is divided into two parts or surfaceareas. This division may be.

eiiected by the shape of the electrode, or by a substance coating onepart which has different electrical properties from those of the surfaceof the other part, or by an auxiliary electrode system fixed adjacent tothe output electrode.

In such forms the line of demarcation is the line of division of the twoparts.

In. each of these forms the output signals are produced by theoscillation of the electron beam across the line of demarcation underthe influence of input signals, which are usually applied to a pair ofelectrostatic deflection plates. The efficiency of the valve depends onthe smallness of the deflection of the electron beam necessary toproduce signals of a given amplitude, since this controls theamplification produced by the valve. If the deflection necessary toproduce output signals of the required amplitude. is very small thensmall changes in the location of the electron beam due toaccidentaldisturbances in the valve will cause intolerable disturbances in theoutput. For example, when the deflection sensitivity of the beam valveis high, minute changes of the bias potentials of the deflection platescan result in a displacement of the electron image which is of the orderof the width of said electron image, and thus the image may be displacedright ofi the output electrode. In such a case the valve may stopfunctioning altogether. If. therefore, a high amplification is to beobtained, it is important that the effect of such accidentaldisturbances should be eliminated.

There is always an optimum mean position of the image. The presentinvention provides an electrical circuit whereby the eflect oraccidental disturbances on the output is substantially eliminated, andwherebythe image automatically is kept substantially in this optimummean positlon, and the invention consists, in general, of an electricalcircuit including an electronic valve device containing means forproducing an electron beam and deflection means to which electricsignals may be applied in order to deflect said electron beam, whereinmeans are provided for feeding on to said deflection means an electricalsignal produced. by said electron beam on an electrode of saidelectronic valve device due to any disturbance which tends to deflectsaid electron beam, whereby the deflection of the electron beam whichsaid disturbance tends to produce is substantially eliminated.

In the operation of the invention a signal produced by; the displacementof the electron "beam due to an accidental disturbance is fed on to adeflection plate of the valve in such a way that the displacementof theelectron beam is counteracted or reduced, thereby reducing thedisturbance produced in the output.

The signal which is thus fed back may be derived from the outputelectrode or it may be produced on an auxiliary electrode adjacentto theoutput electrode. In either case it is .fed on to the afore-mentionedplate of the valve through any convenient impedance which impedance maybe part of an impedance bridge through which the potential of thedeflection plate .is defined.

Although the amplification of the valve has been stressed herein, theinvention .is nevertheless not confined to use in connection with avalve employed as an amplifier. It is applicable to the type of valvedescribed iffit is, desired to eliminate the efiects of accidentaldisturbances when the valve is applied to other purposes, e. g.

normal output signals.

In certain adaptationsoi the beam valve, for

instance as a detector, arrangements may advantageously be made wherebythe width of the electron image is automatically controlled to a desiredvalue. The relative ratio of the first and second anode potentials ofthe focussing system of the electron beam may be automatically adjustedby signals developed on one or more of the electrodes of the beam valve.

Reference will now be made to Figure l, which shows a high frequencyamplifier circuit including a deflection modulated cathode ray valve Iof the type described in our United States application S. No. 403,914,filed July'24, 1941, Patent No. 2,313,886, dated March 16, 1943. Signalsto be amplified. are fed through a tuned circuit H on to a deflectionplate 12 of the valve H1. The potential variations thusproduced on thedeflection plate 12 cause an electron beam, produced by a cathode [3, agrid 14, and a first anode l5, and focussed by a second anode IE on toan output electrode IT, to oscillate across the output electrode [1,thereby producing output signals across the output impedance 18. Theoutput electrode I1 is of the type which is divided into two parts. Asuppressor grid lies adjacent the part He, and is maintained at apotential negative rela tive to the output electrode, so that when theelectron beam falls on the part Ila, all secondary electrons aresuppressed, and the output electrode is charged in a negative sense.Adjacent the part 11b is a grid 2| which is maintained at a potentialpositive relative to the output elec trode, so that when the electronbeam falls on the part l'ib the secondary electrons are collected by'thegrid 2|, and the output electrode is charged'in a positive sense. A moredetailed description of the operation of this output electrode will befound in the afore-mentioned United States application S. No. 403,914.

When the electron beam falls partly on the part 11a and partly on thepartv l'lb, the rate of charging of the output electrode is theresultant of the rate of negative charging of the part Ila and the rateof positive charging of the part Nb, and may be either positive ornegative or zero. For the circuit of Figure l, the optimum mean positionof the electron image on the output electrode is that which correspondto .zero charging of the output electrode.

" The automatic control of the position of the electron beam is affordedby the resistance l9.

:This is the simplest form which the automatic control according to thepresent invention can take. This resistance l9 connects the outputimpedance l8 to the potential tap of the second anode l6, while theoutput impedance is also connected through the resistance 23 to thedeflection plate I2. .The A. C.'signals produced in the impedance l8 aredecoupled to earth through the decoupling condenser 22, so that only D.C. signals and signals of relatively low frequency from the outputelectrode pass through the resistances l9 and 23. The condenser 22 alsodecouples any input signals ,which pass through the resistance 23. Whenthe electron beam falls in the optimum mean position,- there is no D. C.

I the disturbance.

signal on the output electrode. tential of the deflection plate [2 andthe mean potential of the output electrode I! are second anodepotential.

If, however, the electron beam becomes disof potential, iscommunicatedto the deflection plate l2 through the resistance 23, whichshould be much higher than the impedance of the cir- "cuit H, and thisdeflects the electron beam back towards the optimum mean position,thereby sub-, stantially eliminating the displacement due to If thedisplacement is towards the positive part Ilb of the output electrode,the output electrode becomes charged in a positive sense,and the changeof potential thu produced is communicated to the deflection plate [2,there by deflecting the beam back towards the optimum mean position asbefore. I I

The actual resulting displacement andchange of potential of the outputelectrode may readily be calculated. For example, suppose the beamcurrent of the electron beam is ib, and that the current falling on thepositive part 11b of the output electrode is multiplied by secondaryemission by a factor 1,0, while that falling on. the negative part Ilais multipliedby a factor (p. Let the deflection sensitivity of thedeflection plate l2 on the electron beam be denoted by Ds, and supposethe disturbance causing the displacement of the electron beamcorresponds to a displacement y of the beam. Denote the resultingdisplacement of the beam by A, and the change of potential of the outputelectrod by v. Let the width of the electron image be denoted by 2a andthe value of the resistance l9 by R. The displacement A is the resultantof the displacement y and the counter-displacement produced by thechange of potential v communicated to the deflection plate l2. Thiscounter-displacement is v.Ds. Thus:

A==yv.Ds (l) The displacement A causes a current to flow to the outputelectrode of which the magnitude is: ib.( +1//).A/2a. The change ofpotential 12 thus produced across the resistance R. is given by:

v=R.ib.(+ .A/2a (2) Substituting this value in (l) and transforming,

we obtain:

1+Ds.R.ib.(+i//)/2a l+ R where ,u is the mutual conductance of thevalve. Hence, from (2):

Thus the po- 7 Thus the resulting displacement is only 1/150,0U0 of themagnitude than it would be if the automatic image control were notemployed. Also, if the disturbance corresponds to a displacement y of 5times the image width, i. e. 1 mm. in the'abo've example, then thechange in the .mean potential of the output electrode is v=0.2 volt,which is quite unimportant.

' In Figure 1 the earth point is shown as being the point to which thegrid I4 is connected, but this is unimportant; any of the electrodes l3,l4, 1'5, l6 could be chosenas the earth point.

It should also be noted that the second anode I6 is shown connected to aless positive potential than the first anode It; This procedure is notessential, but has nevertheless certain advantages. In the first placethe less positive potential of the second anode, which is equal or verynearly equal to the potential of the deflection plate l2, gives greaterdeflection sensitivity to the deflection plate. Also in the circuit ofFigure 1 the output electrode is connected to second anode potential.The grid 2| must be more positive than the output electrode, and it iseconomical to connect the first anode also tothis more positwopotential. Furthermore the use of the most positive available potentialfor the first anode produces the minimum of aberrations in the electronimage formed by the electron beam.

It has been assumed above that the optimum mean position of the electronbeam corresponds to the position of zero charging of the outputelectrade. This assumption requires some further comment.

The mean position of the electron beam can be changed without aiiec'tingthe amplification of the valve. The input acceptance of the valve isactually greatest if the centre of the beam falls on the line ofseparation of the positive .and negative parts of the output electrodein the mean position; this only corresponds to the position of zerocharging if 4: and l are equal. If, however, the beam is adjusted tosome mean position which does not correspond to the position of zerocharging, then a D. '0. current flows permanently to or from the outputelectrode through the resistance 19. This produces a potentialdifierence across the resistance 1 9, and this resistancemust 'beconnected to a potential difiering from second anode potential'by anamount equal to the aforesaid potentialdifierence in order that thedeflection" plate |2 shall be on second anode potential. This fact is ofno consequence, apart from considerations regarding simplicity of thecircuit, if the beam current ib is constant during operation of thevalve, but if the beam current is altered by adjusting the volumecontrol, then the current in the resistance l9 also changes,therebychanging the potential difference across the resistance. Thischange in the potential diiference must be compensated either bychanging the value of the resistance |9 suitably or by adjusting thepotential tapping to which it is connected. This additional adjustment imost undesirable.

It should .be noted that, in the circuit of Figure 1, no preliminaryadjustment of the automatic control circuit is necessary. The electronbeam is automatically set to the optimum mean position when the valve isswitched on.

Figure 2 shows an audio frequency amplifier circuitincluding adeflection modulated cathode ray valvev 25 of the type described in ourco pending patent application Ser. No. 447,277. In

common with the circuit of Figure 1 input siz nals in the circuit 'ofFigure 2 are applied to a deflection plate l2 of the valve, wherein an Ielectron beam is generated and focussed by a cathode l3, grid M, firstanode |5, and second anode 5 which function in the same way as theelectrodes similarly numbered in Figure "The input impedance, acrosswhich the input signals are produced, is in Figure 2, however, aresistance 26, and the output signals are likewis developed across aresistance 21. The output electrocle 29, from which the output signalsare :obtained, is of thesingle homogeneous type. The secondary electronsemitted from the output eieo trode 29 under the influence of theelectron beam are collected by a grid 2|, which is maintained at apotential more positive than the output electrode. The output electrodeis always charged in one sense only by the electron beam, positive ifits secondary emission coefficient is greater than unity and negative ifits secondary emission coefiicient is less than unity. In what followsit will be assumed that the secondary emission coeflicient is greaterthan unity, but conditions are exactly the same in principle if thesecondary emission coeflicient is less than unity. Automatic control ofthe electron image according to the invention is effected by meansof'the resistances 23, 30 and 3|. signals and signals of relatively lowfrequency produced on the outputelectrode 29 pass through theseresistances, the A. C. signals corresponding to the input signals beingdecoupled through the decoupling condenser 22. Any input signalsmentioned patent application.

which pass through the resistance 23 are decoupled by the decouplingcondenser 28. g

The output A. C. signals are produced from the output electrode 29 byoscillation of the elec-'- tron beam across the edge of the outputelectrode, thereby varying the amount of current passing from the outputelectrode 29 through the output resistance 21. A more completedescription of the action of the output electrode system is given in thespecification of the afore- The optimum mean position about which theelectron beam should oscillate is that position in which half theelectron beam falls on the output electrode. Thus there is a permanentD. 0. current passing to the output electrode. This current passesthrough the output resistance 21 and the resistance system 3|, 30, tothe supply potentiometer 32, and, when the electron beamialls in theoptimum mean position, the magnitude of this D. C. current is: i29=/ztbsp, where vzb is the electron beam current and l/ is themultiplicationfactor produced by secondary emission pro.- duced by the outputelectrode 29. The mean potential of the output electrode is definedrelative to the point G of the potentiometer 3|, 30, which connects thepoints A and H of the supply potentiometer 32, by the magnitude of. thecurrent 2'29 and the value of the resistance .21. The potential of thepoint G is in turn determined by the potentials of the points A and H,

the values of the resistances 30 and 3|, and the magnitude of thecurrent 229 flowing through theresistance system 3|, 30. The meanpotential of the output electrode may be set at a convenient value byadjusting the -tapping point A on the supply potentiometer 32. The pointB of the potentiometer 3|, 30 is connected'through the resistance 23 tothe deflection plate 12, .so

that the. deflection plate l2 acquires the potential of the point B. Inthe optimum working Only the D. C.

thence to the deflection plate l2. This more positive potential on thedeflection plate pulls the electron beam back towards the optimum meanposition, thereby substantially eliminating the effect of thedisturbance. The change in the mean potential of the output electrode isquite unimportant, being of the order of one volt.

It may be shown that the resulting displace-1 ment A caused by adisturbance corresponding to a displacement y of the beam is given by:

y 1+,J2B 1+R30 R31 where #:Dsib tD/Za is the mutual conductance of thevalve, and RB, R30, R3l are respectively the resistance between Band H,the value of the resistance 30, and the value of .the resistance 3|. Thechange of potential v of the output electrode is given by:

1 y. .R30.(l+R27/R30+R27/R31) Ds. 1+R3o R31+,..RB where R21 is the valueof the resistance 21. for example we take:

Ds=5 mm./volt. ib=0.2 milliamps. 0.2 mm.

y=1.0 mm. RB=100,000 ohms. R27=300,000 ohms. R30=400,000 ohms.R31=1,600,000 ohms.

then we obtain: A =:l//2,000

12:1.55 volts.

The operation of the automatic beam control device is the same apartfrom the sense of the deflection and potential changes if thedisturbance causes the electron beam to be displaced further oil theoutput electrode.

If the circuit of Figure 2 is employed in the audio frequency range, itis desirable that the decoupling condenser 22 should have a-low im- Ip'edance above 50 cycles/sec. and a high impedance below 50 cycles/sec.Thus it may conveniently be replaced by a high-pass filter with acut-cit just above 50 cycles/sec. In order to counteract any microphonyin the valve, it is possible to place an additional tuned circuit inseries with 22 which is tuned to the microphonic frequency, so that thisfrequency is not decoupled but is fed through the automatic beam controlsystem. Signals of this microphonic frequency produced on the outputelectrode 29 are thereby counteracted, so that the eiTect of themicrophony is substantially eliminated.

Figure 3 shows a high frequency amplifier circuit. including adeflection modulated cathode ray valve 33 of the type described in ourco-pending application. The output electrode 34 is of the singlehomogeneous type, but, in contradistinction to the output electrode 29in Figure 2', it is adapted to be charged in a positive sense bysecondary emission from itself or in a negative sense by secondaryemission from an auxiliary electrode 35. A more complete description ofthe operation of this output electrode system is given in thespecification of the aforesaid application.

The circuit of Figure 3 is the same as that of Figure 1 in all essentialparticulars, except that the resistance l9 which afiords the automaticbeam control according t the present invention is not connected to theoutput impedance I8, but instead is connected to an auxiliary electrode36. When the electron beam falls in the optimum mean position, thiselectrode 36 intercepts a fraction of the beam current. Advantageouslyone edge of the electrode 36 coincides with the centre of the electronbeam when the beam is in the optimum mean position. The fraction of thebeam current intercepted by the electrode 36 causes a current to flow inthe resistance I9, therebyestablishing a potential diiference across theresistance I9. Thetapping J at which this resistance is connected to thesupply potentiometer 32 should be so adjusted that the resultingpotential supplied to the deflection plate I2, when the electron beam isin the optimum mean position, is second anode potential. If, now, adisturbance deflects the beam from the optimum mean position, thecurrent reaching the electrode 36 changes, thereby causing the potentialdifference across the resistance l9 to change. The potential supplied tothe deflection plate 12 is thus changed in such a way that the effect ofthe disturbance is substantially eliminated.

In the circuit of Figure 3, the automatic beam control isindependent ofthe output impedance, so that themean potential of the output electrodecan beset at any desired value, by adjusting the tapping K at which theoutput impedance is connected to the supply potentiometer 32, withoutreference to the potentials required by the automatic beam controlsystem. The independence of the automatic beam control and the outputimpedance has the further advantage that, since the resistance IS in theautomatic beam control circuit is independent of the output impedance,the beam current employed is not limited by the requirements of theautomatic beam control system, as it is, for example, in the circuit ofFigure 2, where the resistances 3|, 30 of the auto- 'beam controlsystem.

The circuit of Figure 3 is particularly suitable for use where theoutput impedance l8 consists of a pure capacity, as, for example, whenthe circuit is used as a Kerr cell amplifier.

The automatic beam control circuits shown in Figures 1 to 3 aredescribed by way of example only, and the invention is not restricted tothe exact form of circuits there shown. Also the circuit shown inconnection with any one output electrode system is not applicable onlyto that output electrode system, nor does any one output electrodesystem require to be operated with the type of circuit shown inconjunction therewith.

For example, the automatic beam control circuit shown in Figure 1 isapplicable without modiflcation to the output electrode ssytem shown inFigure 3. v

In the circuits of Figures 1 to 3, the automatic beam control has beenshown operating with the aid of an electrostatic deflection plate. Thisdeflection plate can be replaced by an electromagnetic deflection coilif desired.

What We claim and desire to secure by Letters Patent is:

1. In an electrical circuit, the combination with a multiple electrodeelectronic valve device including electrode means for producing anelectron beam, and deflection means to which alternating currentelectric signals may be applied in order to deflect said electron beamsof frequency selective means for feeding on to said deflection means anelectrical potential produced by said electron beam on an electrode ofsaid electronic device due to a disturbance of other than signalfrequency which tends to deflect said electron beam, whereby theundesired deflection of the electron beam which said disturbance tendsto produce ma be substantially eliminated.

2. In an electrical circuit, the combination with an electronic valvedevice, an input circuit upon which electric signals may be impressed,an output circuit, said electronic valve device including means forproducing an electron beam and deflection means connected to said inputcircuit for deflecting the beam with respect to output electrode meansto which said output circuit is connected; of means for suppressinginadvertent deflection of the beam by disturbances of non-signalfrequency; said last means including a network in said output circuitfor feeding to said deflecting means in degenerative sense thecomponents of the output circuit potential variations of non-signalfrequency. I

3; In an electrical circuit, the invention as recited in claim 2,wherein said output electrode means comprises an output electrode, saidoutput circuit being connected-to said output electrode.

4. In an electrical circuit, the invention as recited in claim 2,wherein said output electrode means comprises an output electrode and anauxiliary electrode, and said output circuit includes an outputimpedance connected to said output electrode, said network beingconnected to said auxiliary electrode.

5. In an electrical circuit, the combination with an electronic valvedevice including means for producing an electron beam and deflectionincluding resistance means connecting said output impedance to saidsource of energizing potential, and circuit connections between saidresistance means and said deflection means to impose in degenerativesense upon said deflection means potentials of non-signal frequencydeveloped across said resistance means.

6. In an electrical circuit, the combination with an electronic valvedevice including means for producing an electron beam, an outputelectrode, means including an anode for focusing the beam in the regionof the output electrode by applying to said anode a direct currentpotential, and an electrostatic deflection plate on which the energizingpotential during operation of the device is substantially equal to thepotential of the anode, of an output impedance across which outputsignals may be produced in response to input signals applied to saiddeflection plate, a resistance network including a resistance connectingsaid output impedance to said anode and a second resistance connectingsaid output impedance to said deflection plate, so that any disturbanceof non-signal frequency which tends to deflect said electron beamproduces across said first resistance an electric potential which is fedthrough said second resistance on to said deflection plate, therebysubstantially eliminating the deflection of the electron beam which thedisturbance tends to produce.

7. In an electrical circuit, the invention as recited in claim 6,wherein said resistance network is connected to earth through adecoupling condenser so that feed-back of potentials of input signalfrequencies to said deflection plate MARCUS JAMES GODDARD.

